Let me tell you first how I was introduced to this daylight saving time first.
It was 2001. I went to work as usual, and the manager gave me a look, saying why are u late by an hour? I looked at the clock and said, i'm not late. She pointed to the wallclock, and I said with a very confident tone, that clock is wrong! Then they kind of figured out that I didn't know about the time changed and told me that the time has been changed. well, living in bangladesh i never heard of it and had no clue that time can be changed in some part of the world. so, she had a real hard time trying to explaining what time change is! guess what, it was april 1, 2001. I was april fooled by... by whom? i could not figured it out yet.

when I asked her why do u guys do it, the time change thing, she didn't know the answer. not only that, I asked many other people about it and no one knew why the time has to be changed.
the only explanation i heard that make sense so far is, at some time when agriculture depended on daylight, farmers used to work as long as possible when the day light stays. but then, because it was late enough, all the stores, grocessaries and all were closed. to solve this problem, the daylight saving time was introduced. even though this is not necessary anymore, the tradition is being kept.

is this the only reason for so much hassle? or is there any other real reason?

AS, the answer of your query is already in the title of your thread- time is changed in certain part of the world only to save and to maximise the use of day light and working hours. Check the link to learn more about daylight saving time.